Spinning process

ABSTRACT

A method of spinning fiber-forming material comprising forming three frustoconical portions, each having an apex angle larger than the foregoing section, and including a cylindrical portion downstream, the frustoconical portions being divergent to the upstream end thereof, said method permitting the production of lower denier material at a lower drawdown with superior mechanical properties and being characterized by ease of mechanical production to minimize jet deposits and prolong jet life.

United States Patent Joseph Germano Santangelo Morristown, NJ.

[72] Inventor 21' Appl. No. 885,996 22 Filed Dec. 17, 1969 I23] Division of Ser. No.1750,839, Aug. 7, 1968,

abandoned, which is a continuation-in-part of Ser. No. 336,683, Jan. 3, 1968, Pat. No.

[45] Patented Sept. 21, 1971 [73] Assignee Celanese Corporation New York, N.Y.

[54] SPINNING PROCESS 11 Claims, 3 Drawing Figs.

[52] US. Cl 264/176, 264/184, 264/205, 264/207 [51] Int. Cl B28b 3/20, DO1f3/26 [50] Field ofSearch 18/855; 264/206, 176, 177, 200, 207

[56] References Cited UNITED STATES PATENTS 3,210,451 10/1965 Manning et al. 264/200 3,365,528 1/1968 Riley 264/225 Primary Examiner-Jay H. Woo AttorneysT. J. Morgan, S. D. Murphy and Andrew F. Sayko,

ABSTRACT: A method of spinning fiber-forming material comprising forming three frustoconical portions, each having an apex angle larger than the foregoing section, and including a cylindrical portion downstream, the frustoconical portions being divergent to the upstream end thereof, said method permitting the production of lower denier material at a lower drawdown with superior mechanical properties and being characterized by ease of mechanical production to minimize jet deposits and prolong jet life.

SPINNING PROCESS This application is a divisional of U.S. application Ser. No. 750,839 filed Aug. 7, 1968 now abandoned, which in turn is a continuation-impart of U.S. application Ser. No. 336,683 filed .lan.9, 1964, now U.S. Pat. No. 3,537,135.

BACKGROUND OF THE INVENTION The present invention relates to a novel spinning process.

In spinning a man-made fiber-forming material such as cellulose triacetate into filaments, a liquid comprising the polymer, i.e., a solution of the polymer in an appropriate solvent or a molten composition containing the material, is extruded through fine capillary orifices. While satisfactory products have been obtained with orifices having profiles heretofore used, the formation of these orifices is often difficult and costly and/or their use in the spinning process results in various process disadvantages, e.g., the formation of excessive amounts of deposits in the orifices resulting in high pressure drops across the spinneret and necessitating the use of larger than desirable orifices which have a diverse effect on fiber properties, and difficulties in starting up the process.

In dry spinning, since the filaments are not normally given an after-stretch, the major orientation imparted to the fiber takes place in the vicinity of the jet. Since fiber properties are related to the degree of orientation, it is desirable to have a detailed understanding of this mechanism.

The flow profile or velocity distribution of the fluid leaving the jet is a function of the orifice design. The pressure distribution throughout the orifice is also related to orifice design. If we assume that the major flow pattern, e.g., smooth flow lines vs. turbulence, is translated down to the smaller element, the molecule, then a smooth flow pattern through the orifice will orient the molecules along their major axis whereas turbulence would produce random nonoriented molecules.

An analysis of orifice design, as related to velocity and pressure distributions, shows that the flow lines are smooth and undisturbed over the continuous portion of the orifice. It was found that when the polymer flow meets an angle or other discontinuous surface, eddy currents and turbulence set in. This condition becomes worse as the velocity of the polymer through the orifice is increased. These conditions are not conducive to molecular orientation and disrupt molecular alignment. The correct rate of change of curvature eliminates this disruption and improves yarn properties and this same mechanism also contributes to a reduction in jet corrosion.

The ideal solution to the problem of turbulence is a jet with a smooth hyperbolic approach to the orifice. This design minimizes flow turbulence and produces greater orientation in the yarn. To produce pure hyperbolic holes in a spinneret would be extremely difficult and impractical, but the novel technique developed by applicant is an excellent inexpensive approximation. Yarn tenacity, elongation and jet deposits are unexpectedly improved with a decrease in turbulence caused by a decreases in the orifice incidence angle. Therefore, the preferred jet design for both quality and productivity, especially with regard'to jet deposits, combined a smooth hyperbolic approach and an incidence angle which approaches zero.

It is an object of this invention to provide a process for the formation of man-made fiber-forming materials such as cellulose triacetate into filaments using an improved spinning process.

It is a further object of this invention to provide a spinning process using a novel jet or spinneret whereby the problem of turbulence in spinning filaments is eliminated, as evidence by a reduction in jet deposits, a reduction in pressure drop across the spinneret and the production of yarn having extremely high tensile properties.

It is a still further object of this invention to provide novel jets or spinnerets having a specified profile which may be produced using a relatively simple manufacturing operation.

Other objects will be apparent from the following detailed description and claims wherein all parts are by weight unless otherwise indicated.

DISCUSSION OF THE PRIOR ART The spinneret of this invention represents an improvement over the prior art spinneret disclosed in U.S. Pat. No. 3,210,451, to Manning, issued on Oct. 5, 1965, on an application filed on Dec. 1, 1960. This patent is assigned to the assignee of the present application. In addition to the advantages of Manning's spinneret, applicants apparatus and process significantly reduce jet deposits which cause great pressure drops across the spinneret and allow the production of high tenacity and high elongation fibers by utilizing a smooth approach to the capillary. Jet deposits tend to form when there is a sharper line of demarcation between the smallest or first frustoconical section and the bottom cylinder or capillary.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention, a fiberforming material, such as cellulose triacetate or cellulose secondary acetate, is formed into filaments by extruding a liquid comprising such material, e.g., a solution of such material in an appropriate solvent or a molten composition containing such material, through an orifice having a cylindrical portion communicating with the outlet face of the spinneret and three frustoconical portions which are divergent toward the inlet side of the spinneret, with the apex angle of each frustoconical portion being larger, the farther away it is from the cylindrical portion. Thus, if the frustoconical portion adjacent to the cylindrical portion is termed the first frustoconical portion, then the second frustoconical portion adjacent to the first has an apex angle larger than that of the first and the third frustoconical portion adjacent to the second on the inlet side has an apex angle greater than that of the second.

The first frustoconical portion, i.e., that communicating with the cylindrical portion preferably has an apex angle of less than about 17, e.g., 12 to 17, and most suitably in the range of 16 to 17; the secondfrustoconical portion communicating with the first frustoconical portion preferably has an apex angle of at least 13 greater than the apex angle of the first frustoconical portion and most suitably in the range of 25 to 35; and the third frustoconical portion communicating with the second frustoconical portion preferably has an apex angle of at least 30 greater than that of the second frustoconical portion and most suitably in the range of 60 to 65.

The use of an orifice having the above-described profile allows for an orifice size, e.g., expressed as diameter, of the cylindrical portion, which is smaller than usual. The use of smaller holes, e.g., as low as 0.025 mm., allows for the production of lower denier material, e.g., as low as l denier per filament, produced at a lower drawdown or spin draw ratio, defined as the ratio of the denier of the fiber-forming material being extruded to the denier of the taken up material. This type of material is very desirable for certain uses, e.g., cigarette filters. Moreover, smaller holes with the concomitant employment of smaller drawdown ratios also result in superior mechanical properties, e.g., tenacity and elongation.

The term cylindrical" is employed herein for the jet face section of the orifice design since it connotes a generally regular cross section, as distinguished from the diameters of the remaining sections, but it is understood that such cross section may be circular or any noncircular configuration conventional in this art such as triangularcross sections, square cross sections, Y cross sections, l-beam cross sections, X cross sections. trilobal cross sections and the like.

Suitably, the length of the cylindrical portion along the axis of the spinneret is about one-half to 10, preferably 12 to 1% times the diameter of the cylindrical portion, the length of the first frustoconical portion is about A to 1 times the diameter of the cylindrical portion; the length of the second frustoconical portion is about 3 to 8 times the diameter of the cylindrical portion, and the length of the third frustoconical portion is about 20 to 30 times the diameter of the cylindrical portion.

Preferable ranges of linear values for the dimensions of each portion of the orifice are as follows: about 0.025 to 0.50 mm.,

preferably about 0.025 to 0.060 mm. for the diameter of the cylindrical portion; about 0.0125 to 0.50 mm., preferably about 0.0125 to 0.060 mm. for the length of the cylindrical portion; about 0.030 to 0.040 mm. for the length of the first frustoconical portion; about 0.1 to 0.23 mm. for the length of the second frustoconical portion; and about 0.76 to 0.89 mm.

' (i.e., about 30 to 40 mils) for the third frustoconical portion.

A particularly desirable spinneret of the type described above is one having orifices each with a cylindrical portion having a circular cross-sectional diameter no greater than about 0.034 mm. and a length of about 1% times the diameter of the cross section, a first frustoconical portion having an apex angle of about 17 and a length of about 1 times the diameter of the cylindrical portion, a second frustoconical portion having an apex angle of about 30 and a length of about 6 times the diameter of the cylindrical portion, and a third frustoconical portion having an apex angle of about 60 and a length of about 22.5 times the diameter of the cylindrical portion, all the lengths being measured along the axis of the orifice.

The process is of particular value in the dry-spinning of cellulose triacetate from solution in a solvent comprising a major amount of a halogenated hydrocarbon.

Novel spinnerets of this invention may be made without frequent breakdown of drilling tools by first countersinking a hole with a tool having an angle equal to that of the third frustoconical portion, the depth of such hole corresponding to the length desired for such third frustoconical portion. A drilling or countersinking tool having an angle corresponding to the second frustoconical portion, i.e., less than that of the first tool used, is then inserted into the hole and used to further drill a hole to an increased depth corresponding to the desired length of the second frustoconical portion. A cylindrical tool is inserted into the hole and used to drill the cylindrical portion of the orifice which extends entirely to the outlet face of the spinneret. Finally, a punch is used to form the first frustoconical portion by pressing down the circle of intersection between the second frustoconical portion and the cylindrical portion, using a punching tool with an angle corresponding to the desired first frustoconical portion. After the first operation resulting in the formation of a cone-shaped hole including a part corresponding to the third frustoconical portion, the placing of each drilling tool is simplified by the fact that it need only be inserted into an already formed hole.

It can be seen that when using the above-described method, the relatively weak drilling tools, i.e., the tool used to drill the cylindrical portion and the frustoconical portions of smaller apex angles, are only employed to drill relatively small proportions of the total thickness of the spinneret plate. This has the effect of drastically reducing breakage of the drilling tools.

The cylindrical portion of the orifice may be punched rather than drilled, in which case such section may have, in addition to a circular cross section, cross sections of other shapes, such as a triangular cross section, a square cross section, etc., de-

pending upon the shape of the punching tool.

Contemplated under this invention are spinnerets having plates with thicknesses up to about 7.62 mm., i.e., about 300 mils. However, to avoid an unduly large amount of breakage of drilling and/or punching tools, particularly when the spinneret is'to be used in a dry spinning process, a plate having a relatively small thickness is suitably used, e. g., no greater than about 1.016 mm., i.e., about 40 mils, and most suitably in the range of about 0.635 to 1.016 mm., i.e., about 25 to 40 mils. Moreover, the use of a spinneret plate of small thickness has the further advantages that it results in lower pressure drop across the spinneret plate making spinning easier and reduces the chance of blockage of the orifice.

As mentioned previously, the process of this invention is particularly useful in the dry spinning of cellulose esters, such as the spinning of cellulose triacetate from solution in a solvent comprising a major proportion of a halogenated hydrocarbon. The process may be suitably carried out using fairly high spinning speeds using 100 to 1,000 meters per minute to produce filaments having a denier in the range, for example, of l to 10 denier per filament. However, deniers outside of this range may also be obtained.

As employed herein, cellulose triacetate has reference to cellulose acetate having fewer than about 0.29 and preferably fewer than about 0.12 free hydroxyl group per anhydroglucose unit of the cellulose molecule, i.e., an acetyl value calculated as combined acetic acid by weight of at least about 59 percent and preferably at least about 61 percent.

Advantageously its intrinsic viscosity ranges from about 1.5 to 2.5 and is preferably about 2, and it is present in the dope to a concentration ranging from about 20 to 25 percent. In place of methylene chloride, the dope solvent may comprise other halogenated lower alkanes such as ethylene dichloride or propylene chloride. Advantageously, up to about 15 percent by weight of the dope solvent comprises a lower alkanol such as methanol, ethanol, isopropanol, etc. The preferred dope solvent is methylene chloride-methanol in the proportions of about -10 by weight.

The process of this invention is also especially useful in the dry spinning of cellulose secondary acetate from solution in a solvent such as acetone. Cellulose secondary acetate, as employed herein, has reference to cellulose acetate having an acetyl value in the range from 54 to 56 percent, preferably between 54 and 55 percent, calculated as combined acetic acid.

For convenience, the invention has been described and illustrated with reference to the dry spinning of cellulose triacetate, but it should be understood that both the process and apparatus are applicable to the spinning of other fiberforming materials by wet, dry or melt spinning such as polyamides, polyesters, acrylics, vinyl chloride and vinylidene cyanide polymers and the like. Since the essential operative principle stems from rheological rather than chemical or mechanical characteristics, and suitable dimensional adaptations may easily be achieved within the context of such systems.

BRIEF DESCRIPTION OF THE DRAWINGS The invention may be further illustrated with reference to the accompanying drawing wherein:

FIG. 1 is a plane view ofa section of a spinneret used in accordance with this invention with the orifices arranged in a circle around the periphery of the spinneret plate and their size exaggerated to indicate their appearance;

FIG. 2 is a sectional view showing the profile of the contemplated orifices, and;

FIG. 3 is a schematic illustration of a dry spinning operation.

Referring now more particularly to the drawing, FIG. 1 shows a spinneret or jet plate 10 as viewed from the inlet side with orifices l 1 each of which has the appearance of four concentric circles corresponding to the largest diameter of the orifice at the inlet face of the plate and the circles of intersection of the various frustoconical portions and the cylindrical portion, at the outlet side of the spinneret plate.

As shown in FIG. 2 illustrating the profile of the contemplated orifice of spinneret 10, the wall of the cylindrical portion is indicated at 13 with numeral l4, l5 and 16 identifying the walls of the first, second, and third frustoconical portions of the orifices respectively.

In Figure 3 there is shown a dry spinning cabinet 17 to which dope is supplied through a pipe 18, being extruded through the spinneret 10 of FIGS. 1 and 2. Hot air is admitted to the cabinet 17 at 19 and is exhausted at 20 along with vapors of the dope solvent. The filaments 21 leaving spinneret 10 pass about a guide 22 and leave the cabinet at 23 being pulled as a yarn 24 by draw rolls 25. The yarn 24 passes through a guide 26 and is twisted and taken up on a bobbin 27 by a conventional collector such as ring spinner 28.

In addition to the fact that smaller orifices may be used in carrying out the process with the advantages described above, the process of this invention results in the formation of substantially less jet deposits than when various other orifice shapes are used, particularly in the case of the dry spinning of cellulose triacetate from solution in a solvent comprising a major proportion of a halogenated hydrocarbon. Moreover, the employment of the orifice profile of this invention results in considerably longer jet life, a more uniform filamentary product (e.g., in terms of cross section) with better properties, e.g., of tenacity and elongation that is the case when spinnerets are employed with more conventional orifice designs. Improved dyeing properties may also be obtained.

Finally, the process of the invention using the distinct orifice shape as described above may be started up much more easily than other spinning processes, and makes possible the employment of higher spinning speeds without deterioration of filament properties.

The following example further illustrates the invention:

EXAMPLE 1 A 22 weight percent solution of fiber-forming cellulose triacetate having an acetyl value of 6 1 .5 percent by weight calculated as combined acetic acid in a solvent mixture consisting of 91 percent of methylene chloride and 9 percent of methanol was extruded through a chromium plated stainless steel spinneret with a plate having a thickness of 1.016 mm. and with 5 orifices arranged in a circle each with a profile as indicated in FIG. 2. Cylindrical portion 13 of each orifice had a circular cross section with a diameter of 0.034 mm. and a length of 0.018 mm. First frustoconical portion 15 had an apex angle 17 and a length of 0.035 mm.; second frustoconical portion 16 had an apex angle of and a length of 0.20 mm.; and third frustoconical portion 17 had an apex angle of 60 and a length of 0.762 mm., each of the lengths being measured along the axis of the orifice. The resulting filaments passed through air in a spinning cabinet at C. and were taken up on a bobbin at a linear speed of 500 meters per minute after being withdrawn from the spinning cabinet. The yarn had a denier of 3.75 d.p.f., a tenacity of 1.35 grams per denier and an elongation of 35 percent.

After 24 hours of continuous operation from the time that the spinneret was installed, the jet deposits resulted in a reduction in orifice area equal to only 1.7 percent of the total due to deposited material when observed at 400 magnification. This represents a substantially smaller formation of jet deposits than is obtained when orifices of more conventional profile are used.

EXAMPLE [1 A 22 weight percent solution of fiber-forming cellulose triacetate having an acetyl value of 61.5 weight percent was extruded through the chromium plated stainless steel spinneret of example 1 utilizing the procedure of example 1. The resulting filaments pass through air in a spinning cabinet at C. and were taken up on a bobbin at a linear speed of 350 meters per minute after being withdrawn from the spinning cabinet.

A 22 weight percent solution of fiber-forming cellulose triacetate having an acetyl value of 61.5 percent was extruded according to the procedure of the example of U.S. Pat. No. 3,210,451, Manning, utilizing the spinneret disclosed therein.

The resulting filaments were passed through air in a spinning TABLE 1 Prior Art Jet-plated Jet of this invention-plated Boiled 3 Hrs. in Methylene Chloride:

Average 2.60 Average 1.40

Cellulose triacetate filaments extruded according to the foregoing procedures was put on cones and beams and data collected for a period of six months. Data comparing efficiency and tensile properties of filaments extruded utilizing the Manning spinneret with filaments utilizing the spinneret and process of this invention are shown in table 11 below:

TABLE 11 Prior Art Jet of this Plated Invention-Plated Bleb Rate/M lbs. 4.5 3.4 Part-runs, 5.0 3.9 Tenacity, g.p.d. 1.23 1.25 Elongation, 7a 31 31 Major Lindly/BTY 230 Beam Rejection, 3.1 2.8 Cone Rejection, 7a 5.5 4.5

EXAMPLE [[1 Fiber-forming cellulose triacetate was extruded according to the procedure of example 1 utilizing unplated stainless steel spinnerets having the dimensions of the spinneret of example 1. The resulting filaments were passed through air in a spinning cabinet at 25 C. and were taken up on a bobbin at a linear speed of 500 meters per minute after being withdrawn from the spinning cabinet. C.

Cellulose triacetate was extruded according to the procedure of the example of U.S. Pat. No. 3,210,451, Manning, utilizing an unplated spinneret having the dimensions of the spinneret of the said example. The resulting filaments were passed through air in a spinning cabinet at 25 C. and were taken upon a bobbin at a linear speed of 500 meters per minute after being withdrawn from the spinning cabinet.

A comparison of the jet deposit data for jets run for 24 hours utilizing the process of this invention and the prior art process and jet of U.S. Pat. No. 3,210,451 is shown in table 111 below:

TABLE III Percent deposits Jet (l-lnch x 5-ho1e x Aver- 0.032 mm.) Jet A Jet B age Run:

1 Prior art-unplated 9. 0 14. 0 1t. 5

Grand average 10. 2

4 Jet of this inventlonunp1ated 1. 4 6.0 3. 7

EXAMPLE IV A 22 weight per cent solution of fiber-forming cellulose triacetate having an acetyl value of61.5 percent by weight calculated as combined acetic acid in a solvent mixture consisting of 91 percent of methylene chloride and 9 percent of methanol was extruded through an unplated stainless steel spinneret at a jet face temperature of 80 C. The spinneret having a plate with a thickness of 1.016 mm. and with 20 orifices arranged in a circle each with a profile as indicated in H6. 2. Cylindrical portion 13 of each orifice had a circular cross section with a diameter of 0.028 mm. and a length of 0.018 mm. First frustoconical portion 15 had an apex angle 17 and a length of 0.035 mm.; second frustoconical portion 16 had an apex angle of 30 and a length of 0.20 mm.; and third frustoconical portion 17 had an apex angle of 60 and a length of 0.762 mm., each of the lengths being measured along the axis of the orifice. The resulting filaments passed through a 12-foot updraft in a spinning cabinet at 35 C. and were taken up on a bobbin at a linear speed of 300 meters per minute after being withdrawn from the spinning cabinet. The yarn was wound onto one pound packages and had an average tenacity of 1.33 grams per denier and an average elongation of 49.0 per cent.

Spinning speeds in excess of 1,000 meters per minute are easily achieved utilizing the process and spinneret of this invention. In addition, the life of the spinneret in use ranges from about 1,000 to 1,500 hours, as compared with a useful life of 600 hours for the prior art Manning spinneret.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for spinning manmade fibers by forming a spinnable liquid of a fiber-forming material selected from the group consisting of cellulose esters, polyamides, polyesters, acrylic polymers, vinyl chloride polymers and vinylidene cyanide polymers and passing said liquid in the form of a stream through a spinnerette orifice of a spinnerette or jet plate, the

' improvements comprising (1) converging said stream in a first zone into an initial frustoconical stream at a defined apex angle in a smooth flow pattern, (2) passing said stream to a second zone and further converging said initial frustoconical stream at a second apex angle at least 30 less than said defined apex angle into an intermediate frustoconical stream, (3) subsequently passing said stream to a third zone and further converging said intermediate frustoconical stream at a third apex angle at least 13 less than said second angle, said third angle being about 17 or less, into a final frustoconical stream, (4) passing said stream to a fourth zone and forming said stream in a continuing smooth flow pattern into a cylindrical stream, (5) passing said cylindrical stream out of said fourth zone and (6) solidifying said stream into filamentary material.

2. The process of claim 1 wherein said fiber-forming materia1 is a cellulose ester in the form of a spinnable solution thereof.

3. The process of claim 2 wherein said fiber-forming material is cellulose secondary acetate.

4. The process of claim 2 wherein said fiber-forming material is cellulose triacetate.

. The process of claim 1 wherein said defined apex angle is about 60 to 65, said second apex angle is about 25 to 35 and said third apex angle is about 12 to 17.

6. The process of claim 2 wherein the cellulose ester is dispersed in a solvent comprising a major proportion of methylene chloride and up to about 15 percent by weight of a lower alkanol.

7. The process of claim 2 wherein the filaments formed are taken up at a linear speed of at least 300 meters per minute.

8. The process of claim l wherein the initial frustoconical stream has a length of about 20 to 30 times the diameter of the cylindrical stream; the intermediate frustoconical stream has a length about 3 to 8 times the diameter of the cylindrical stream; the final frustoconical stream has a length of about one half to 1 times the diameter of the cylindrical stream; said cylindrical stream having a diameter of about 0.025 to 0.50 millimeters and a length about one half to 10 times its diameter.

9. The process of claim 8 wherein said cylindrical stream has a diameter of up to about 0.060 millimeters and a length about one half to lltimes its diameter.

10. The process of claim 9 wherein said cylindrical stream has a circular cross sectional diameter no greater than about 0.034 millimeter and alength of about one half times its diameter, the initial frustoconical stream has an apex angle of about 60 and a length of about 22.5 times the diameter of the cylindrical stream, the intermediate frustoconical stream has an apex angle of about 30 and a length about 6 times the diameter of cylindrical portion, and the final frustoconical stream has an apex angle of about 17 and a length of about one times the diameter of said cylindrical stream.

11. The process of claim 16 wherein said defined apex angle is about 60, said second apex angle is about 30 and said third apex angle is about 17. 

2. The process of claim 1 wherein said fiber-forming material is a cellulose ester in the form of a spinnable solution thereof.
 3. The process of claim 2 wherein said fiber-forming material is cellulose secondary acetate.
 4. The process of claim 2 wherein said fiber-forming material is cellulose triacetate.
 5. The process of claim 1 wherein said defined apex angle is about 60* to 65*, said second apex angle is about 25 to 35* and said third apex angle is about 12 to 17*.
 6. The process of claim 2 wherein the cellulose ester is dispersed in a solvent comprising a major proportion of methylene chloride and up to about 15 percent by weight of a lower alkanol.
 7. The process of claim 2 wherein the filaments formed are taken up at a linear speed of at least 300 meters per minute.
 8. The process of claim 1 wherein the initial frustoconical stream has a length of about 20 to 30 times the diameter of the cylindrical stream; the intermediate frustoconical stream has a length about 3 to 8 times the diameter of the cylindrical stream; the final frustoconical stream has a length of about one half to 1 times the diameter of the cylindrical stream; said cylindrical stream having a diameter of about 0.025 to 0.50 millimeters and a length about one half to 10 times its diameter.
 9. The process of claim 8 wherein said cylindrical stream has a diameter of up to about 0.060 millimeters and a length about one half to 1 1/2 times its diameter.
 10. The process of claim 9 wherein said cylindrical stream has a circular cross sectional diameter no greater than about 0.034 millimeter and a length of about one half times its diameter, the initial frustoconical stream has an apex angle of about 60* and a length of about 22.5 times the diameter of the cylindrical stream, the intermediate frustoconical stream has an apex angle of about 30* and a length about 6 times the diameter of cylindrical portion, and the final frustoconical stream has an apex angle of about 17* and a length of about one times the diameter of said cylindrical stream.
 11. The process of claim 16 wherein said defined apex angle is about 60*, said second apex angle is about 30* and said third apex angle is about 17*. 